1. Field of the Invention
The present invention generally relates to free-space optical communications systems, and, more specifically, to an apparatus for mounting free space optical communications system equipment to a window or window frame.
2. Background Information
With the increasing popularity of wide area networks (WANs), such as the Internet and/or the World Wide Web, network growth and traffic has exploded in recent years. Network users continue to demand faster networks and more access for both businesses and consumers. As network demands continue to increase, existing network infrastructures and technologies are reaching their limits.
An alternative to present day hardwired or fiber network solutions is the use of wireless optical communications. Wireless optical communications utilize point-to-point communications through free-space and therefore do not require the routing of cables or fibers between locations. Thus, wireless optical communications are also known as free-space or atmospheric optical communications. For instance, in a free-space optical communication system, a beam of light is directed through free-space from a transmitter at a first location to a receiver at a second location. Data or information is encoded into the beam of light, and therefore, the information is transmitted through free-space from the first location to the second location.
A conventional free-space optical system is shown in FIGS. 1A and 1B. The free-space optical system includes a pair of terminals (i.e., transceivers) 110 that are typically located on or in separate buildings or towers, such as depicted by buildings 111 and 112. Each terminal 110 includes a primary collector 113 to which a secondary mirror 114 is coupled via a plurality of rigid struts 116. The terminals further include a transmitted signal lens 118 mounted within secondary mirror 114, and a set of transmitter/receiver optics and electronics 120. All of components 113, 114, 116, 118, and 120 are operatively coupled to a yoke that is connected to a base 122 via a gimbal assembly, such that these components are all moved in response to a gimbaled movement of the yoke relative to a static surface on which the base 122 is placed. In the illustrated configuration, terminals 110 are disposed in respective office in buildings 111 and 112, and the optical signals transmitted and received by the terminals pass through windows 134 and 136.
With reference to FIG. 1B, data is transmitted from a 110T to a terminal 110R in the following manner, wherein the suffix xe2x80x9cTxe2x80x9d indicates components corresponding to transmitter operations, and the suffix xe2x80x9cRxe2x80x9d indicates components corresponding to receiver operations. An optical signal 124 is generated by transmitter/receiver optics and electronics 120T of terminal 110T and directed through and opening 126T defined in primary collector 113T towards transmitted signal lens 118T, which produces a collimated signal 128. As collimated signal 128 moves toward terminal 110R, in the width of the signal diverges very gradually. As will be recognized by those skilled in the art, the divergence of the various optical signals depicted in the Figures contained herein are exaggerated for clarity. Upon reaching terminal 110R, the outer portions of collimated signal 128 impinge upon primary collector 113R, which comprises a concave mirrored surface that redirects those portions of the signal that impinge upon it toward secondary mirror 114R, while an inner portion 132 of the collimated signal is substantially blocked. Collimated signal 128 is then reflected by secondary mirror 114R towards the secondary mirror""s focal point 130, where it is received by transmitter/receiver optics and electronics 120R.
The convention terminal mounting technique that employs the base and gimbaled assembly discussed above has several drawbacks. One drawback is that since the base is typically mounted on a floor, the terminal is susceptible to floor motion, such as vibrations caused by people and/or equipment in offices or rooms in which the terminal is located. The conventional terminal is also somewhat obtrusive, occupying a significant amount of office space. Furthermore, the conventional mounting technique enables users to potentially cause damage to a terminal and interfere with received or transmitted signals.
The present invention provides an apparatus and method for mounting a free-space optical communications system (FSO) equipment, such as a terminal, to a window. The apparatus includes a substantially rectangular frame member in which a central opening is defined. In one embodiment, the frame member comprises an extrusion that may be cut to a desired length to fit various window widths. The frame member is coupled to a window frame or the window via a plurality of universal mounting brackets that are disposed toward respective corners of the frame member. A support that is operatively coupled to the frame member provides a mounting interface to couple the frame to an FSO terminal that is disposed within the central opening. In one embodiment, the support comprises a gimbaled support that enables the FSO terminal to be rotated about a pair of orthogonal spin axes and then locked into place once a desired pointing is obtained. In typical installations, the apparatus is mounted toward the top of a window frame and a valance is provided to prevent undesired access to the gimbaled support and FSO terminal and make the apparatus appear less obtrusive.